1. Field
The present invention relates to elevators and elevator traction sheaves as discussed below.
2. Description of Related Art
The operation of a conventional traction sheave elevator is based on a solution in which steel wire ropes serving as hoisting ropes and also as suspension ropes are moved by means of a metallic traction sheave, often made of cast iron, driven by an elevator drive machine. The motion of the hoisting ropes produces a motion of a counterweight and elevator car suspended on them. The tractive force from the traction sheave to the hoisting ropes, as well as the braking force applied by means of the traction sheave, is transmitted by the agency of the friction between the traction sheave and the ropes.
The coefficient of friction between the steel wire ropes and the metallic traction sheaves used in elevators is often insufficient in itself to maintain the required grip between the traction sheave and the hoisting rope in normal situations during elevator operation. The friction and the forces transmitted by the rope are increased by modifying the shape of the rope grooves on the traction sheave. The traction sheaves are provided with undercut or V-shaped rope grooves, which create a strain on the hoisting ropes and therefore also cause more wear of the hoisting ropes than rope grooves of an advantageous semicircular cross-sectional form as used e.g. in diverting pulleys. The force transmitted by the rope can also be increased by increasing the angle of bite between the traction sheave and the ropes, e.g. by using a so-called “double wrap” arrangement.
In the case of a steel wire rope and a cast-iron or cast-steel traction sheave, a lubricant is almost always used in the rope to reduce rope wear. A lubricant especially reduces the internal rope wear resulting from the interaction between rope strands. External wear of the rope consists of the wear of surface wires mainly caused by the traction sheave. The effect of the lubricant is also significant in the contact between the rope surface and the traction sheave.
To provide a substitute for the rope groove shape that causes rope wear, inserts placed in the rope groove to achieve a greater friction coefficient have been used. Such prior-art inserts are disclosed e.g. in specifications U.S. Pat. No. 3,279,762 and U.S. Pat. No. 4,198,196. The inserts described in these specifications are relatively thick. The rope grooves of the inserts are provided with a transverse or nearly transverse corrugation creating additional elasticity in the surface portion of the insert and in a way softening its surface. The inserts undergo wear caused by the forces imposed on them by the ropes, so they have to be replaced at intervals. Wear of the inserts occurs in the rope grooves, at the interface between insert and traction sheave and internally.